1. Field of the Invention
This invention relates to blowers using an impeller to draw in and centrifugally accelerate a fluid for controlled discharge thereof.
2. Background Art
Portable power blowers are widely used by homeowners and professionals, particularly in the landscape and maintenance industries. The most popular version of the power blower is a hand-holdable, gas powered unit which uses a forwardly projecting discharge conduit that can be conveniently oriented to control air discharge by an operator in use. An impeller, with a laterally extending rotational axis, draws air inwardly as it rotates. In one construction, the impeller has an unbladed core volume with radially projecting blades having upstream ends at the core volume and downstream ends located radially outwardly therefrom. Operation of the impeller causes air to be drawn into the core volume, picked up by the blades, centrifugally accelerated in a volute, and diverted at a point of separation from the downstream ends of the blades at high volume to the discharge conduit.
The assignee herein offers a line of such blowers which are lightweight and capable of producing a high volume air discharge. One significant problem with these gas powered blowers is that they generate a significant amount of noise during operation. Designers are constantly seeking ways to attenuate the noise generated at different locations throughout the unit to make it more environmentally compatible.
The assignee herein has done a substantial amount of research regarding noise generation in this type of blower. One noise source is where laterally/axially directed incoming air encounters the impeller and abruptly stops and changes direction to a radial flow. The radial flow is in turn abruptly halted and redirected to a curved flow path around the impeller axis in the volute as the radial flow encounters the surface bounding the volute. This abrupt halting and redirection of air flow produces unwanted noise.
Another problematic noise source is at a branching location where the accelerated flow in the volute divides to be either a) directed through the discharge conduit or b) redirected into the volute for recirculation. Directly between these divided flow paths, the accelerated air is abruptly halted, which may generate significant noise as the impeller blades travel past this location and shear the air. Also, the air re-entering the volute passes through a restriction, where the volute has its smallest volume. The noise generation thereat can be reduced by enlarging the volume of the volute at the re-entry point. However, by doing this, the efficiency of the unit may be compromised. Thus, designers in the past have generally opted to produce a more efficient unit while contending with a significant amount of operating noise.
Aside from the noise generated by the air flow and air shearing by the impeller blade in operation, the gas powered drives for these impellers generate noise that must be independently contended with. Conventional two cycle engines generate a significant amount of noise in operation. Communities are now legislating to restrict noise levels to below those which many existing two cycle engines used on power blowers operate at. Whereas, in the past, noise reduction in this field was desired, this noise reduction is now becoming a necessity. The search for solutions to the noise problem has, or is soon likely to, become a priority for most manufacturers of this type of equipment.
One manner of reducing noise generation is to use a motor to drive the impeller which operates off of an AC or DC power source. The use of AC power may be impractical where a source of AC power is unavailable or not readily accessible.
With respect to DC power sources, current technology is such that DC power sources, portable enough to be moved in a practical manner with the equipment that is powered, have a relatively limited life before recharging is required. Equipment efficiency is paramount in systems operating using a DC power supply.